Incineration provides a safe and effective method of destroying hazardous wastes. Such wastes generally include pyrotechnics, explosives, and propellants, collectively known as "PEP". Pyrotechnics are powders that burn at less than the speed of sound. Explosives are typically defined as any chemical compound, mixture or device, the primary purpose of which is to function by explosion, i.e., with substantially instantaneous release of gas and heat. The waste may also include configured munitions and reactive waste. Configured munitions are devices with PEP contained within. For example, configured munitions include, but are not limited to, ammunition, mortar shells, fuzes, detonators, grenades, and rocket motors, and so forth. Reactive waste is typically a solid waste exhibiting the characteristic of reactivity as defined by 40 C.F.R. .sctn. 261.23. Examples of reactive waste include, but are not limited to, scrap propellants, scrap explosives, scrap pyrotechnics, sludge, and reactive soil and debris.
Incineration involves the exposure of the waste material to high temperatures for extended periods of time. The purpose of this exposure is to oxidize the material rather than detonate it. Due to the composition of hazardous waste, toxic gases are usually emitted during the oxidation or combustion of the waste material. Due to their toxic nature, such emissions are tightly regulated. Therefore, the emissions must be treated to meet regulatory requirements.
Incineration of the hazardous waste described above may be accomplished by several methods. Because temperature at the point of oxidation may reach approximately 3000.degree. F., and pressures from detonation may reach one to three million pounds per square inch at the point of detonation, the most common incineration method involves the use of a specially designed rotary kiln. Most common rotary kiln incinerators for hazardous waste are lined with refractory material and mounted on an incline to move materials through the kiln. However, such kilns are not satisfactory for incinerating items that might detonate when burned because of the damage it does to the refractory material. The rotary kiln developed by the U.S. Army for destruction of bulk explosives and propellants, and configured munitions is mounted horizontally and is an unlined, thick walled, cast steel kiln with internal helical flights as part of the casting that push the materials through the kiln as it rotates.
The material to be burned is fed into one end of the kiln and is pushed toward the exit end of the kiln by the rotation of the kiln. A fuel oil fired burner at the exit end of the kiln provides the heated air and the flame to burn the material in the kiln. The heated air and flame is pulled toward the entrance end of the kiln by an induced draft fan at the end of an associated air pollution control system (APCS). Temperatures within the kiln are supplemented by the oxidation of the explosive wastes.
The Army's rotary kiln, designated as the Ammunition Peculiar Equipment (APE) 1236 Deactivation Furnace (DF), consists of four five-foot long retort sections bolted together, with a nominal diameter of 3 feet, and wall thicknesses between 21/4 and 31/4 inches. The rotary kiln is rotated on trunions driven by a variable speed drive system. As the kiln rotates, internal spiral flights propel the feed material through the retort. The spiral flights also prevent sympathetic explosive propagation between the areas of the kiln divided by the spiral flights. Typically, the flights are spaced 30 inches apart and average 10 inches in height.
The material is introduced into the APE-1236 kiln by either a continuous feed system or a positive feed system. The continuous feed system utilizes a two-section straight conveyor system leading to the kiln entrance and feeds the kiln a continuous stream of waste material. Due to the straight configuration of these conveyors, a premature explosion by the waste upon entering the kiln could cause the primary conveyor to buck back toward the kiln operators. The positive feed system utilizes steel boxes to carry batches of bulk waste material. The steel box is placed on a conveyor which carries it to a transfer station, where the box is moved laterally in front of the kiln ingress. A ram then pushes the box into the kiln. The material inside the box is oxidized and the box is recovered at the kiln exit for reuse after cooling.
The feed housing on the APE-1236 is designed such that change between the use of the conveyor feed system and the positive feed system requires the removal of a lower portion of the gravity feed chute when the positive feed system is used, and replacing that portion when using the conveyor feed system. To make this change requires shutting down the furnace, and allowing it to cool before personnel can physically make the change. Also, the APE-1236 feed chute is located in a larger housing that periodically needs to be emptied of the munitions items that are kicked out of the kiln by the detonation of other items. There is a large door in the front of the feed housing that is opened to gain access to clean the housing and to also gain access to the lower portion of the feed chute for change out. The ram and transfer conveyor of the positive feed system must be moved out of the way to open the feed housing door.
The air pollution control system for the APE-1236 kiln consists of a primary exhaust vent and shroud, said shroud extending over the entire length of the kiln and over the feed chute. The primary exhaust vent draws exhaust gas from the inside of the kiln. The shroud attempts to contain fugitive emissions escaping from between the retort sections or from the ingress or egress of the kiln. Air is pulled into the shroud through vents by the combustion air blowers for the primary burner and secondary combustor. The primary exhaust or flue gas from the kiln is taken to a secondary combustor. The secondary combustor can raise the temperature of this exhaust or flue gas to approximately 1880.degree. F. for 1 second, attempting to oxidize any unburned waste material in the gas, such as unburned reactive materials, or principle organic hazardous constituents (POHC). The APE-1236 achieves a 99.99% destruction removal efficiency (DRE). The exhaust then passes through a high temperature gas cooler, a low temperature gas cooler, a cyclone, a baghouse in which most particulate matter is eliminated, an induction draft fan, and then exits to the atmosphere through an exhaust stack.
The APE-1236, however, requires operational limitations and other limits on what materials can be incinerated in it to comply with environmental standards. Specifically, the APE-1236 has no provisions to control the acidity of emissions. Thus, feed rates involving heavy metals such as lead, cadmium, or those producing acid gases must be based on the allowable emissions from these metals, or acids, rather than on the greater capacity of the kiln to handle the reactivity of the material being fed. The APE-1236 also fails to adequately control the emission of particulates.
Therefore, a need exists for an incinerator that safely and effectively destroys the entire family of PEP, configured munitions and devices, and hazardous reactive wastes at efficient rates based on the limits of the incinerator, not the emission regulations. The incinerator must be capable of exposing the waste materials to high temperatures for an extended period of time. The incinerator system must also be capable of withstanding the accidental detonation of the wastes. The system must also be designed to control the emission of toxic gases which are the by-products of the burning waste. This control system must be able to detect "upset"situations at any location of the incinerator system and respond accordingly. The control system must also be capable of being updated to meet ever changing regulations. Most importantly, the incinerator must be designed to protect the safety of its operators from both explosions and toxic emissions.